A planar light source device using an optical semiconductor element (an LED), in which a large number of grooves having a shape of a semicircle on cross section are formed concentrically in order to scatter light, is reported (see, for example, reference 1).
[Reference 1] JP 2000-184137 A
However, in the planar light source device described above, sufficient uniformity of light emission in a plane has not been obtained yet.
It is an object of the present invention to provide a direct-type backlight that has a more uniform amount of light emission in a plane.